Kate praised for down-to-earth 'mum moment' with kids at the polo

It's easy to think of Kate Middleton as a royal first and a mum second, but her trip to the polo with her three children this week proved the opposite.

Though we're used to seeing her dressed to the nines at lavish events, Kate looked totally at home sat on the grass while she picnicked with Prince George, Princess Charlotte and Prince Louis out of the boot of their car.

Kate Middleton with Prince Louis, Princess Charlotte and Prince George attend the King Power Royal Charity Polo Match. (Getty)

With little Louis, one, in her lap, the Duchess of Cambridge watched on happily as her two eldest children played in the car's flat boot, snacking out of Tupperware as they did.

Charlotte, four, chowed down on snacks out of a plastic lunchbox while she sat on the edge of the boot, her legs swinging down.

Meanwhile older brother George, five, rolled over the back sets and stood playfully at the car's edge, holding onto the lid of the boot as he swung around.

While some royal mums may have been mortified by the children's playful attitudes, Kate's laid-back parenting style was on display as she sat happily with Louis and let the children enjoy their day out.

“Kate is a fantastic mum,” one onlooker told People. “She was calm with the children.”